1. Field of the Invention
The present invention relates to a robot for conveying a substrate, for example, a substrate conveyer robot suitable for use in conveying a semiconductor wafer substrate to place it in a container such as a cassette, and to take it out from the container.
2. Related Art
Conventionally, a wafer substrate conveyer robot of the belt link type has an arm expansion/contraction mechanism with first through third arms, in which the gear ratio of the pulley furnished on the rotation spindle of each arm is 2:1:2. This type of robot conveys the substrate horizontally by the control of only two axes. One of them is a robot advancing/retreating axis R for linearly advancing and retreating the third arm by the belt link mechanism, and the other one is a robot revolving axis θ for revolving the rotary base of the robot. Further, with lifting/lowering of all arms, the robot inserts and removes the substrate to and from the cassette.
In general, a substrate conveyer robot 01 possesses an arm expansion/contraction mechanism composed of three arms 05, 07, 09, and the two control axes, i.e., the robot revolving axis θ and the robot advancing/retreating axis R. As illustrated in FIG. 11, the center of the substrate 030 held by a hand 010 fixed on the third arm 09 advances and retreats along a straight line J0 that passes through the center of a rotary shaft (=a first spindle; this is positioned on the same axis as the robot revolving axis θ) of the first arm 05. Thus, the substrate conveyer robot 01 is designed to convey and insert the substrate 030 only into a cassette 032 that is disposed with its face centered on the line J0. Here, the straight line J0 coincides with the robot advancing/retreating axis R.
The cassette 032 is in the shape of a quadrangle, and permits the substrate 030 to be inserted only from one direction perpendicular to the plane of the opening thereof. In the case of the conventional robot with two axes, as illustrated in FIG. 11(a) through FIG. 11(c)), the robot 010 or cassette 032 has been required to be disposed in such a manner that the center line of the cassette 032 perpendicular to the aperture plane passes through the robot revolving axis θ (the pivotal center). A rotation base 03 is rotatable around the robot revolving axis θ, so that the third arm 09 can be positioned perpendicular to the front of the cassette 032. The third arm 09 is advanced and retreated linearly along the robot advancing/retreating axis R (the straight line J0), thereby inserting and taking out the substrate 030 to and from the cassette 032. In other words, the control of the rotating movement around the robot revolving axis θ and the control of the advancing and retracting movement along the robot advancing/retreating axis R have been carried out sequentially, not simultaneously.
As described above, most of the conventional robots possessing two control axes, the robot revolving axis θ and the robot advancing/retreating axis R, presumably, do not combine the control of rotation around the robot revolving axis θ with simultaneous control of the advancing and retracting along the robot advancing/retreating axis R. Therefore, the conventional robots could only insert and remove the substrate to and from the cassette that is positioned in a radial manner to (in other words, positioned right in front of) the robot revolving axis θ.
Therefore, in order for the robot to control the insertion and removal of the substrate to and from the cassette, even in case the cassette is positioned on an arbitrary straight line deviating from the robot revolving axis θ, there was no way to use such a robot other than that disclosed in Japanese Patent-Laid-Open No. Hei 11(1999)-33948 Publication. This robot adds one axis to the foregoing two axes (two control axes) to freely control the position and direction of the hand of the last arm in the horizontal plane.
However, the use of the robot disclosed in the above publication requires an extra drive along the additional axis, and at the same time complicates control, thus increasing the cost.
The substrate conveyer robot illustrated in FIG. 11 is a single arm sequence type, having an arm expansion/contraction mechanism composed of three arms operative in a single sequence. However, a double arm sequence type substrate conveyer robot that has (a pair) bilaterally symmetrical arm expansion/contraction mechanisms operative in two sequences has the same problem as described above.